1. Field of the Invention
The present invention relates to a fiber-optic amplifier including a light waveguide piece and a pump light source.
2. Background Information Such a fiber-optic amplifier is known from many sources, for example, from: "ECOC '89", 15th European Conference on Optical Communication, Sep., 10-14, 1989, Gothenburg, Sweden, Proceedings, Vol. 1, Regular Papers TUA 5-7, pages 86-89. The amplifying piece of light waveguide there is an Er.sup.3+ doped light waveguide piece and the light of the pump light source is coupled into the amplifying light waveguide piece by way of a coupler. Two different variations are described there. In the first configuration (co-propagating configuration), the pump light coupler is arranged upstream of the amplifying fiber piece with respect to the transmission direction up to the amplification of the optical signal. In the second configuration (counter-propagating configuration), the coupler for coupling the pump light into the amplifying light waveguide piece is disposed downstream of the light waveguide piece with respect to the transmission direction of the optical signal to be amplified. For the present invention, the difference between the two configurations is of no significance.
The aspect of the fiber-optic amplifier of interest here is its pump light source, more precisely, the wavelength of the pump light generated by the source. T. R. Chen discloses in "Structural and Compositional Control of the Output Wavelength of Very High Power 0.98 .mu.m GaInAs Lasers for Pumping Fiber Amplifiers", in IEEE Photonics Technology Letters, Vol. 3, No. 8, August, 1991, pages 694-696, that the performance of fiber-optic amplifiers equipped with Er.sup.3+ doped amplifying light waveguide pieces is substantially dependent on the wavelength of the pump light generated by the pump light source. Consequently, the wavelength of the light generated by the pump light source should lie at 980 nm with a tolerance of 2 nm. Various measures are described for taking care that during the manufacture of a certain semiconductor laser its wavelength lies in that range.
Even if it is accomplished, during the manufacture of the semiconductor laser, that its emission wavelength lies precisely at or near the wavelength that is suitable as pump light for the fiber-optic amplifier, difficulties may nevertheless arise if the semiconductor laser is employed, for example, in a fiber-optic amplifier because the emission wavelength may change due to aging of the semiconductor laser or as a function of the ambient temperature. The cited publication does not discuss these difficulties but concerns itself only with how the desired wavelength can be realized as accurately as possible during manufacture.